Composite structures are used in a wide variety of applications. In aircraft construction, composites are used in increasing quantities to form the fuselage, wings, and other components of an aircraft. During the operational life of an aircraft, the wings are exposed to a variety of environmental effects. For example, during flight when the aircraft is moving forward at high speed, the leading edge of the wings may be subjected to impingement by rain and other forms of moisture. In addition, the aircraft including the wings may be subjected to lightning strikes.
Conventional methods for protecting a composite leading edge from rain impingement include fastening a protective metallic strip over the leading edge. Unfortunately, the attachment of a metallic strip to a composite wing is a time-consuming and labor-intensive process requiring a large quantity of mechanical fasteners. The large quantity of fasteners may add to the overall weight of the aircraft. In addition, specialized tooling may be required for maintaining the position of the metallic strip during installation. Furthermore, fasteners that are installed through the outer mold line (OML) surface of the leading edge may disrupt the airflow passing over the OML surface. The disruption in airflow may cause the airflow over the wing to become turbulent with a resulting increase in aerodynamic drag and a corresponding reduction in aircraft fuel efficiency.
In addition, metallic material such as metallic sheet is generally formable into a single-curvature shape by bending the metallic sheet using relatively low-cost tooling. However, the leading edge of a wing may have one or more regions of compound curvature along the length of the leading edge. The process of forming a metallic erosion strip to match the compound curvature of a wing leading edge may require complex metal-forming equipment that may add to the overall cost and complexity of wing assembly.
Regarding protection from lightning strikes, composite materials generally have low electrical conductivity with limited ability to dissipate electrical energy from a lightning strike. Metallic sheeting mounted to the surface of a composite structure may provide some protection in the event of a lightning strike by dissipating electrical energy. Unfortunately, the mounting of metallic sheeting over the surface of a composite wing for lightning protection may involve the same drawbacks associated with mounting a metallic strip over the wing leading edge for erosion protection.
As can be seen, there exists a need in the art for a method of providing a metallic layer over a composite surface without the need to mechanically fasten a separate metallic sheet to the composite article. In addition, there exists a need in the art for a method of providing a metallic layer over a compound curvature surface that avoids the need for complex metal-forming equipment. Furthermore, there exists a need in the art for a method of providing a metallic layer that may protect a composite structure against the effects of erosion, lightning, and other effects.